Noise that affects electrical and/or electronic components flows in through a power line that transmits power to an electric and electronic system and a signal line that receives and outputs an electrical signal from and to the electric and electronic system. Accordingly, an electrical and/or electronic system protecting circuit is installed between the power line and an internal electronic component or between the signal line and the internal electronic component. The electrical and/or electronic system protecting circuit is so important as to say that it is required by almost all electronic products including electron components.
A 800KV-SF6 gas insulating switch gear (GIS) used in a substation, being an example of the electric and/or electronic components, is a high-voltage switch that blocks power transmission when electric leakage occurs in an electric and/or electronic system at a predetermined portion of a power-transmission line or an end portion thereof or when excessive current flows due to a sudden unexpected circumference. The SF6 gas is an insulating gas having a dielectric constant at least two times greater than that of the air.
When the switch is opened or closed because of an unexpected accident, spike current greater than a transmitted voltage may flow in the electric and/or electronic system at this time, the insulating gas or hardenable synthetic resin is destroyed, and the temperature of the switch increases, leading to an explosion of the switch. Additionally, if the substation is struck by lightening, a high-voltage line and the switch may be broken. If these things happen, power transmission should suspend, causing great economical losses. Therefore, an insulator destruction monitoring system is made to monitor the high-voltage switch.
Insulator destruction occurs because, when a high-voltage noise signal having a voltage greater than a rated voltage, particularly, a super-high voltage noise signal, is applied, current is concentrated through impurities included in an insulating material, causing interruption of uniform flow of current and destruction of an insulating material due to an increase in the temperature of the insulating material. Hence, the super-high voltage noise signal having a voltage greater than the rated voltage should bypassed in order to prevent insulator destruction.
High-voltage noise is generally removed by a varistor which is a semiconductor resistance element. A ceramic varistor formed of ZnO has been used to bypass super-high voltage noise. However, because the ceramic varistor should have a great internal resistance, there is a limit in reducing the size of the ceramic varistor. Furthermore, the ceramic varistor cannot completely remove the super-high voltage noise because of the internal resistance and can only relatively reduce the magnitude of the noise according to the magnitude of the internal resistance. However, the ceramic varistor is the only current solution to remove high-voltage noise.
For example, U.S. Pat. Nos. 5,912,611 and 6,594,133 disclose a serge arrester that arrests serge voltage by using a ceramic varistor similar to the above-described ceramic varistor. However, the serge arrester is unable to remove super-high voltage that is greater than 800KV.